In a musical watch or striking watch, the sound level is a constant preoccupation, since it is necessary to produce a sound signal of sufficient intensity to be heard by the user while ensuring the purity of sound of this complication.
The sound level can be improved through the use of additional exterior elements. The frequency content of the sound produced by a striking watch must be rich in a frequency range between 1 kHz and 6 kHz.
Conventional exterior watch elements do not provide efficient radiation within this range, while higher frequency radiation, typically above 6 kHz, generally does not cause any problems.
A radiating element may be capable of radiating in the 1-6 kHz frequency range only if very strict geometric and dimensional constraints are observed, notably low rigidity and/or small thickness, or surfaces with pierced openings.
These constraints generally conflict with the rules of mechanical watch design, the object of which is to ensure impermeability, notably to dust and water, and the mechanical resistance of a watch to shocks and high external pressure, due, for example, to deep immersion, so as to ensure the maintenance and protection of the watch movement.
There are known solutions for integrating sound generating elements directly in external watch components, to facilitate the transmission of vibrations. However, these solutions provide only a small improvement if the external components are not free to vibrate in their natural modes.
EP Patent No 2367079B1 by the same Applicant describes a solution for allowing the crystal to vibrate freely in its natural vibration modes. This solution is acoustically effective, but difficult to produce and requires highly qualified personnel. The first (lowest frequency) vibrations of the crystal correspond to a dipole sound source, which is efficient mainly above 5 kHz.
CH Patent Application No 700102A2 in the name of FREDERIC PIGUET describes a watch case with a gong and gong holder directly integral with the case middle or back cover of the case.
WO Patent No 00/36473 in the name of Buenter-Sanz-Mulet describes a case including a sealed inner chamber containing the movement and the sound mechanism, and an outer chamber which includes an opening communicating with the exterior of the watch. These two chambers are separated by an water-resistant wall arranged to transmit the sound waves towards the outer chamber.
EP Patent Application No 2228693A1 in the name of Roth & Genta—BULGARI describes a gong holder secured to the crystal, through at least one hole in the crystal.
CH Patent No 706079B1 in the name of RICHEMONT describes an water-resistant case, a sound device with an oscillating assembly comprising a first vibrating member placed inside the water-resistant case, and an excitation mechanism for causing the first vibrating member to vibrate. The oscillating assembly includes a second vibrating member placed outside the water-resistant case and connected to the first vibrating member by a median portion of the oscillating assembly which passes through the water-resistant case, the vibration being transmitted from the first to the second vibrating member to emit a sound audible outside the water-resistant case.